which is best for 9 yr old - 24" or 26" wheels?

Hi all, can I get some advice?
I want to get a new MB for my son, who'll be 9 soon. He's quite tall.
He has outgrown his 20" wheeler, and is using my wife's old 1994 Giant ATX 870 with 26" wheels and a 16" frame. It is a nice light bike, about 11.5 kg
He rides it fine and likes it, but it's just a bit too big for easy mounts/dismounts

I had my heart set on getting him a 24"-wheeled MTB, but the choices are a bit limited and he'll outgrow it in a couple of yrs. the best bike available locally is 12 kg - he test-rode one in the weekend and loved it.
Another bike shop suggested getting 26" bike with a small frame - 14" - and certainly this opens up more options.
He hasn't tried one yet

I don't know which will be best. I thought the 24" bike would be better in terms of overall smaller length, wheelbase, etc, and therefore hopefully more manoevrable

Also, what is the best brand? A couple of people have said Giant is the best in terms of weight and value. I have 'budget' XL framed Giant and Trek 4300, and I probably prefer the Trek.

My son was (and is!) tall for his age. He's always surprised me at how soon he's been able to bump up to the next available wheel size. In your case, I believe it's worth getting your son a test-ride on a 14" frame size with 26" wheels. Find a shop w/one in stock. Your son might try it and actually like it, and that would solve your dilemma.

Just remember that no matter what, kids will outgrow bikes. Mine missed the 20" size altogether, going directly from 16" to 24" wheels. Two seasons later he went to 26" wheels and a 14" frame size. A year later I bumped him to a 15" frame. A year later to 17". A year later to 29er wheels. Now he's taller than I am and rides a larger frame size. Once you get to 26" wheels, you can do frame swaps for awhile as he grows. That's the approach I took, anyway.

I had my heart set on getting him a 24"-wheeled MTB, but the choices are a bit limited and he'll outgrow it in a couple of yrs. the best bike available locally is 12 kg - he test-rode one in the weekend and loved it.
Another bike shop suggested getting 26" bike with a small frame - 14" - and certainly this opens up more options. He hasn't tried one yet.

If he'll get a couple of years out of a bike that he loves, I think that's a good solution. But I agree that you should have him test ride a small-framed 26" just to see if it works for him.

My approach was to buy my kids bikes that fit, rather than ones they would grow into. When my daughter outgrew one my son would get it. When he got to big the nephews got it. One of them we saved for future grandchildren. It was a good-quality bike and it still functions perfectly and is ready to ride.

My parents, on the other hand, wouldn't buy my brothers or I a bike until we were eleven, and then we got a full-size, 3-speed, "English Racer". This was the mid-60's. Their thinking was that we would be mature enough by then to avoid getting badly hurt, and they wouldn't have to buy a series of bikes as we grew. I didn't like their approach. I drove my friends crazy borrowing their bikes until I reached the age of 11.

buy the right size bike for his proportions. if a 24" bike fits him now, it will be fine for now. if you buy a nice bike and take care of it, it can be re-sold and the money put toward his next bike. if you buy a 26" bike, you will need to get one with a frame small enough for him and he'll out-grow that too. bikes with 26" wheels come in frames designed for riders from under 5 feet tall to riders close to 7 feet tall, the difference is the frame size, not the wheel size.